/Engine/Plugins/Experimental/GeometryScripting/Source/GeometryScriptingCore/Public/GeometryScript/MeshPolygroupFunctions.h
Create list of all triangles with the given PolyGroup ID in the given GroupLayer (not necessarily a single connected-component)
static [UDynamicMesh](API\Runtime\GeometryFramework\UDynamicMesh) * GetTrianglesInPolygroup ( [UDynamicMesh](API\Runtime\GeometryFramework\UDynamicMesh) * TargetMesh, [FGeometryScriptGroupLayer](API\Plugins\GeometryScriptingCore\GeometryScript\FGeometryScriptGroupLayer) GroupLayer, int PolygroupID, [FGeometryScriptIndexList](API\Plugins\GeometryScriptingCore\GeometryScript\FGeometryScriptIndexList) & TriangleIDsOut )